Three Trophic Level Interactions in Holly Leaf Miner Populations

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This research addresses the impact of natural enemies and host plant variation on the population dynamics and success of a leaf mining herbivore Phytomyza ilicicola which specializes on American holly. The study is explicitly designed to test the idea that the first (host plant) and third (natural enemies) trophic levels interact to influence herbivore dynamics which can not be understood without simultaneous consideration of both aspects. Preliminary work has shown that leaf miner densities, survivorship, and oviposition preferences show consistent differences among trees, and between suburban and forest understory habitats. These differences provide in effect a natural experiment for testing the impact of enemies and host nutrition on herbivore success. The research effort will focus on four interrelated facets of the problem: 1) host plant quality, specifically variation among trees as resources; 2) density and survivorship responses of herbivores to resource variation among trees, and the mutual impact of resource variation and miner demic variation on oviposition response; 3) the direct influence of natural enemies and the interaction of natural enemies and resources on herbivore success; 4) and the relative influence of genetics, environment, and their interaction on host quality variation. Together, these aspects of the study will help to resolve some uncertainties in our standing of plant/herbivore interactions and may aid in the development of biocontrol strategies in forestry and agriculture.